Endovascular delivery devices are used in various procedures to deliver prosthetic medical devices or instruments to locations inside the body that are not readily accessible by surgery or where access without surgery is desirable. Access to a target location inside the body can be achieved by inserting and guiding the delivery device through a pathway or lumen in the body, including, but not limited to, a blood vessel, an esophagus, a trachea, any portion of the gastrointestinal tract, a lymphatic vessel, to name a few. In one specific example, a prosthetic heart valve can be mounted in a crimped state on the distal end of a delivery device and advanced through the patient's vasculature (e.g., through a femoral artery and the aorta) until the prosthetic valve reaches the implantation site in the heart. The prosthetic valve is then expanded to its functional size such as by inflating a balloon on which the prosthetic valve is mounted, or by deploying the prosthetic valve from a sheath of the delivery device so that the prosthetic valve can self-expand to its functional size.
The usefulness of delivery devices is largely limited by the ability of the device to successfully navigate through small vessels and around tight bends in the vasculature, such as around the aortic arch. Various techniques have been employed to adjust the curvature of a section of a delivery device to help “steer” the valve through bends in the vasculature. Typically, a delivery device employs a pull wire having a distal end fixedly secured to the steerable section and a proximal end operatively connected to an adjustment knob located on a handle of the delivery device outside the body. The pull wire is typically disposed in a pull-wire lumen that extends longitudinally in or adjacent to a wall of the delivery device, for example, a sheath or catheter. Adjusting the adjustment knob, for example, rotating the knob, applies a pulling force on the pull wire, which in turn causes the steerable section to bend.
A drawback of this design is that the delivery device suffers from a phenomenon known as “whipping” when the device is torqued or rotated relative to its central longitudinal axis, for example to adjust the rotational position of the distal end portion of the delivery device, while the delivery device is disposed in a curved anatomical pathway, for example, a blood vessel, while the steerable section is deflected to match the curvature of the anatomical pathway. In the deflected configuration, the pull wire and pull-wire lumen adopt a low-energy configuration along an inside of the curved section of the delivery device. The deflected portion of the delivery device resists rotation around the longitudinal axis because such rotation would move the pull wire away from the inside of the curve. In many cases, this resistance makes rotation impossible as a practical matter. “Whipping” occurs when the user successfully rotates the delivery device: as the handle is rotated, the curved section initially resists, then, as the user continues to rotate the handle, suddenly rotates a full 360° from the initial low-energy configuration to a final (equivalent) low energy configuration. Some prior art devices utilize multiple pull wires or tensioning members to effect positioning of the steerable section in more than one flexing plane relative to the central axis of the device; however, these devices are complicated, and like single pull-wire devices, suffer from “whipping” when rotated. Thus, a need exists for a delivery device with improved torqueability and steerability.